Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
With the proliferation of mobile communication device use, concerns regarding long-term health risks associated with frequent and/or intensive use of handheld mobile communication devices have been on the forefront of regulatory and research communities. The discussions typically focus on the potential increase in risk of developing certain types of brain cancers and/or other maladies, caused by localized heating of brain tissue and/or other biological structures in the head and neck of the user of the mobile communication devices. This heating is the result of absorption of non-ionizing radio frequency (“RF”) radiation from mobile devices, most commonly handheld cellular telephones, held in close proximity to the head, typically to the ear of the user for purposes of voice conversation. The radiation is associated with transmission of the reverse channel (mobile communication device transmit, base station receive) radio signal from the mobile device's antenna.
Within any given time period that the head is exposed to radiation from a proximate mobile device, the amount and extent of this localized heating of brain tissue may be proportional to the amount of radiation absorbed, which is in turn proportional to the average power density of the RF signal incident to the local area. For a given orientation between the mobile device's antenna and the user's head the power density of the transmitted signal is proportional to the reverse channel transmit power. In general, during voice calls (which is typically when the mobile communication device is held to the ear) reverse channel transmit power can vary over a very broad dynamic range and is under immediate control by the mobile device. In turn, the mobile communication device is generally compelled by interoperability standards to adjust reverse channel transmit power, up to its maximum possible output, upon instructions from the serving wireless network and sent on the forward channel (base station transmit, mobile communication device receive) from the serving base station. The wireless network may instruct the mobile communication device to adjust reverse channel transmit power so as to accommodate path loss, interference levels, and other variables in the mobile communication device-base station air interface. Generally speaking, the greater the maximum reverse channel transmit power, the more reliably that transmit power can be adjusted to accommodate extant conditions of these variables on the air interface.
Thus, use of mobile communication devices, especially cellular phones, brings a mixture of conflicting aspects. For example, higher maximum reverse channel transmit power may provide better and more reliable service coverage, but increased transmit power may be associated with increased health risks. A mechanical design that enables the device to be positioned against or close to the ear may reduce acoustic interference and provide greater convenience, but may also result in increased RF energy absorption by the user's head.